I. Field of the Invention
The present invention relates to a multiconductor system for connecting a multiport terminal of one electrical subassembly to a multiport terminal of another electrical subassembly.
II. Background Information
Computer systems comprise a plurality of electrical subassemblies which have multiport terminals that need to be interconnected. On a macroscopic scale, such electrical subassemblies may include central processing units (CPUs), printers, displays, memory devices, modems and the like. Each subassembly has a multiport terminal which must be connected to a corresponding multiport terminal on another subassembly. For example, in FIG. 1 a CPU 10 is shown interconnected to a memory unit 12 by a multiconductor system 14. CPU 10 has a multiport terminal 16 while memory unit 12 has a corresponding multiport terminal 18. Multiconductor system 14 comprises a ribbon cable 20 and a conventional pin connector 22 and 24 located on each end thereof. As is well known to those skilled in the art, connector 22 couples to multiport terminal 16 of CPU 10 and connector 24 couples to multiport terminal 18 of memory unit 12.
A cross-sectional view of ribbon cable 20 is shown in FIG. 2. As may be seen in FIG. 2, ribbon cable 20 comprises a reference plane 26, a plurality of conductors 28 and a dielectric material 30, such as non-reinforced plastic, which operates to hold conductors 28 in spaced relation to ground plane 26 while allowing a degree of mechanical flexibility in the resultant multiconductor system 14.
The state of the art for electrical subassemblies has continued to develop, with the resultant speed of operation of such subassemblies today approaching the microwave (subnanosecond) region of operation. However, although there has been a regular and progressive improvement in the operational characteristics of the electronic subassemblies, there has been a notable lack of development in the multiconductor systems used to interconnect the electrical subassemblies.
As a general principle, air-dielectric structures have been known since the time of Hertz and Marconi. For example, U.S. Pat. No. 1,978,418 issued to Dudley discloses the use of a plurality of air dielectric cables concentrically configured in a multiconductor structure. Air or other gas is employed as an effective dielectric in a space between a central coaxial conductor and a corresponding outer cylindrical conducting shell. The coaxial conductor and outer shell are spaced from each other by use of a spiral ribbon insulator. This structure is not readily adaptable to interconnecting multiport terminals.
More recently, radio frequency transmission waveguides have been developed using air as a dielectric material. One such example may be found in U.S. Pat. No. 2,800,634 issued to Grieg et al. In Grieg et al., a single line conductor is supported on the face of a dielectric strip disposed in spaced parallel relation to a corresponding ground conductor. The dielectric strip is in turn supported by beads or narrow strips of dielectric located laterally of the line conductor. Manufacturing techniques for this type of waveguide include cutting and die stamping operations for short lengths and extrusion techniques for longer lengths. The dielectric is identified as being polystyrene, polyethylene, polytetrafluoroethylene or other flexible insulation of high dielectric quality. The conductive material is identified as being in the form of conductive paint or ink, or other chemically deposited or sprayed conductive material. The purpose of such structure is to provide a low loss transmission waveguide for use at ultra high frequencies. By this system, radio frequency waves are reportedly easily propagated in a mode closely simulating the TEM mode along the line-ground conductor system. There has been no known attempt to employ such a structure as a multiconductor interconnect system.
On a microscopic scale transmission lines are known to be separated from ground planes by an air dielectric on integrated circuit chips, as evidenced by U.S. Pat. No. 4,379,307 issued to Soclof. In this arrangement a V-shaped groove is etched into the surface of a silicon substrate and a series of silicon supporting webs are used to support an aluminum beam in spaced relationship to the surface of the groove, which is itself covered by a conductive coating. As a consequence, an air dielectric is present between the beam and the coating. However, the manufacturing process involved is not applicable to commercially feasible multiconductor interconnect systems.
It is, accordingly, an object of the present invention to provide a very high speed, low loss, multiconductor interconnect system which is applicable to interconnect multiport electrical subassemblies of a computer system and is capable of being mass produced.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.